The present invention relates, in general, to vehicle seats and, more specifically, to adjusters for vehicle seats.
Description of the Art:
Power seat adjusters are a popular option on many automotive vehicles and are frequently offered as standard equipment on higher priced vehicles. Such power seat adjusters are primarily used on the driver's seat and, sometimes, on the front passenger seat of the vehicle to provide selective horizontal fore and aft and vertical movement of the seat as well as seat back recliner movement to accommodate occupants of different size and height as well as to provide a comfortable seating position to suit each occupant's preference.
Such power seat adjusters typically carry a seat support frame which supports the seat bottom and sometimes the seat back of a vehicle seat. The seat support frame is mounted on first and second, spaced track assemblies, each formed of an upper track which is connected to the seat support frame and which is slidably mounted on a lower track anchored to the vehicle floor. A drive mechanism typically includes a bi-directional electric motor which rotates a pair of drive shafts extending outward from the motor to a gear assembly or box mounted on each upper track. In one arrangement, each gear box rotates a lead screw extending longitudinally below each upper track. A drive block is fixedly mounted to each lower track and threadingly receives the lead screw to cause reciprocal, horizontal movement of the upper track and the attached seat support frame upon selective energization of the drive motor and the drive shafts.
Similar drive mechanisms are provided for vertical (up and down) adjustment of the seat support frame and, in a seat adjuster having a seat recliner adjustment mechanism, for angularly adjusting the position of the seat back with respect to the seat bottom. The vertical drive mechanism may also include separate front and rear edge seat adjustment drive mechanisms for selectively tilting the front and rear edges of the seat bottom independent of each other as well as simultaneously to raise and lower the entire vehicle seat or, in some applications, only the seat bottom or cushion.
Each vertical and recliner drive mechanism also includes a drive motor having a rotatable output shaft connected to a gear assembly either directly in the case of the front and rear vertical drive mechanisms or by means of two shafts extending from a single motor to separate gear assemblies mounted on each upper track or on the seat support frame in the case of a seat recliner drive mechanism.
As the various drive motors are mounted between the track assemblies, the drive motor output shafts and the drive shafts connected thereto are typically oriented perpendicular to the axis of the associated lead screw. In order to transmit rotation and drive force between the output shaft of the drive motor and the drive shaft connected thereto to the 90.degree. offset lead screw, each gear assembly or box typically includes a worm gear which is insert molded on one end of the associated lead screw. A worm is rotatably mounted in the gear box housing in meshing engagement with the worm gear and is connected to one of the drive motor output shafts or to one of the drive shafts so as to rotate the worm gear and thereby the lead screw upon bi-directional energization of the selective drive motor. Thus, each drive motor requires a separate gear assembly for each lead screw driven by the drive motor. This results in additional components on the power seat adjuster which add cost and take up valuable space in the already crowded space below a vehicle seat.
The rigid connection between the gears in the gear assembly, the drive shaft motor output shaft, the drive shaft, the lead screw and the drive block also leads to additional problems during assembly and operation of a power seat adjuster. It is inevitable in the manufacture and assembly of a mechanical mechanism, such as a power seat adjuster, that poor dimensional conditions, such as concentricity, TIR, and linear discrepancies from nominal design dimensions, can and typically do occur. These dimensional conditions, without correction, can cause various problems in the operation of a power seat adjuster, such as poor breakaway from a stop position, slow operation of the power seat adjuster in extreme temperatures, excessive wear of the components of the power seat adjuster, uneven operation of the power seat adjuster, and the generation of unpleasant sounds or noise during the operation of the power seat adjuster.
Another aspect of a power seat adjuster which is critical in the use of a power seat adjuster, particularly during excessive forces generated during a vehicle collision, is the requirement for seat integrity. As the occupant's seat belt is frequently attached by a seat belt buckle mounting bracket directly to one of the upper tracks of a power seat adjuster to enable the seat belt to move fore and aft with the upper track, any forces exerted on the occupant during a vehicle collision are transmitted directly through the seat belt buckle mounting bracket to the upper track. These forces cause the upper track to move upward with respect to the lower track and, in the event of excessive force, could lead to a complete pullout or separation of the upper track and the attached seat from the lower track. In order to prevent track separation, seat integrity requirements have necessitated the design of the components of a power seat adjuster and, in particular, the design of the upper and lower tracks with high strength materials and in sufficient thicknesses to resist track separation. However, the ever present goal of cost containment and weight reduction has led to the use of extruded aluminum seat tracks. In order to meet strength requirements, such aluminum seat tracks have been provided in large thicknesses or with steel reinforcements, both of which are undesirable in view of cost and weight reduction goals.
U.S. Pat. No. 5,213,300, assigned to the assignee of the present invention, discloses an extruded aluminum seat track assembly for a power seat adjuster which has elongated abutment surfaces formed in each upper and lower track which engage each other under force loading to resist track separation. In this track assembly, cooperating pairs of abutment surfaces in the form of complimentary, J-shaped hooks are formed in each upper and lower track. The pairs of abutments or hooks are arranged such that one complimentary pair of abutments on the upper and lower tracks are spaced further apart than the other pair of abutments during normal operation of the power seat adjuster. Under high force loading, the first pair of abutments engage to provide a first level of track separation resistance, before the other pair of abutment surfaces engage to further resist separation of the upper and lower tracks.
While effective, such a track configuration requires a complex extrusion and close tolerance control of the position of the various abutments on the upper and lower tracks.
Thus, it would be desirable to provide a power seat adjuster for a vehicle seat which overcomes certain deficiencies found in previously devised power seat adjusters. It would be desirable to provide a power seat adjuster having a unique lead screw actuation which enables certain gear assemblies to be eliminated so as to reduce cost, weight, and space requirements as well as the undesirable noise associated with the operation of multiple gear assemblies. It would also be desirable to provide a power seat adjuster having a unique lead screw actuation which permits the use of lower flex shaft rotation speeds with higher torque to reduce noise and vibration in the power seat adjuster. It would also be desirable to provide a power seat adjuster with a unique lead screw actuation which provides more freedom in designing the mounting positions of the drive motors and the drive shafts. It would also be desirable to provide a power seat adjuster having a self-aligning lead screw actuator which overcomes poor dimensional problems, such as concentricity, TIR, and linear discrepancies in dimensions and positions of various components of the power seat adjuster. It would also be desirable to provide a power seat adjuster having a self-aligning drive nut which overcomes poor dimensional problems encountered in the manufacture and assembly of power seat adjuster components and, further, which eliminates components and the associated assembly time and labor required in prior art power seat adjusters which have a fixed mounting of the drive block to the lower track. It would also be desirable to provide a power seat adjuster having a track assembly formed of extruded, high strength, lightweight aluminum at minimal track section thicknesses which has a strong design to resist separation of the upper and lower tracks under vehicle collision force loads.